1. Field of the Invention
The present invention relates to a method for manufacturing an electronic component, more particularly, to a method for manufacturing an electronic component, for example, an oscillator comprising an electronic element such as a ceramic element and a lead terminal soldered to the electronic element.
2. Description of the Prior Art
FIG. 3 is a front view showing an example of a conventional oscillator which is an electronic component in the background of the present invention and to which the present invention can be applied, and FIG. 4 is a sectional illustrative view thereof. An oscillator 1 which will be referred to as an electronic component includes a ceramic element 2 which will be referred to as an electronic element. The ceramic element 2 includes a rectangular piezoelectric substrate 3 made of ceramic. Circular vibrating electrodes 4a and 4b are formed at the center of one main surface of the piezoelectric substrate 3 and the center of the other main surface thereof such that the piezoelectric substrate 3 is sandwiched therebetween, and the vibrating electrodes 4a and 4b are opposed to each other. A drawing electrode 5a is formed on one main surface of the piezoelectric substrate 3 in such a manner that the drawing electrode 5a extends from one end thereof to the vibrating electrode 4a. Similarly, a drawing electrode 5b is formed on the other main surface of the piezoelectric substrate 3 in such a manner that the drawing electrode 5b extends from the other end thereof to the vibrating electrode 4b. One end of each of two lead terminals 6a and 6b having a belt shape is soldered to each of the drawing electrodes 5a and 5b. An outer member 7 made of an outer resin is formed around the periphery of the piezoelectric substrate 3. However, in this case, the outer member 7 is not formed on the periphery of the vibrating electrodes 4a and 4b, but a cavity 8 is formed around the periphery of the vibrating electrodes 4a and 4b to provide a vibrating space for the vibrating electrodes 4a and 4b.
FIG. 5 is a flowchart showing an example of a conventional method for manufacturing the oscillator 1 shown in FIGS. 3 and 4. In the conventional method shown in FIG. 5, at a step S1, the ceramic element 2 is inserted between one end of the lead terminal 6a and one end of the lead terminal 6b wherein the lead terminals 6a and 6b are spaced at a predetermined interval from each other and extending from a frame (not shown). In this case, one end of each of the lead terminals 6a and 6b is placed on the drawing electrodes 5a and 5b of the ceramic element 2, respectively. At a step S2, a flux is applied to portions where the drawing electrodes 5a and 5b are connected with one end of each of the lead terminals 6a and 6b. At a step S3, the drawing electrode 5a and one end of the lead terminal 6a are connected with each other by soldering. Similarly, the drawing electrode 5b and one end of the lead terminal 6b are connected with each other by soldering. At a step S4, a residual flux remaining on the connected portions is cleaned. At a step S5, a wax 9 is dripped on the periphery of the vibrating electrodes 4a and 4b of the ceramic element 2 at a location corresponding to the cavity 8 to be formed. At a step S6, the outer member 7 and the cavity 8 are formed around the periphery of the ceramic element 2 and so on.
The step S6 comprises a plurality of steps. At a first step, as shown in FIG. 6(A), an outer resin 10 to form the outer member 7 is applied to the periphery of the ceramic element 2 and the wax 9. The outer resin 10 consists of a mixture of a thermosetting resin, a solvent, and a filler. At a second step, by drying the outer resin 10, as shown in FIG. 6(B), the solvent contained in the outer resin 10 is dispersed to the outside, and pores are formed in the outer resin 10 on paths through which the solvent has been dispersed. Then, the whole is heated to 150.degree. C. to harden the outer resin 10. At a third step, when the whole is heated, as shown in FIG. 6(C), the wax 9 is absorbed into the pores formed in the outer resin 10, and the cavity 8 is formed around the periphery of the vibrating electrodes 4a and 4b. At a fourth step, when the whole has been heated to 150.degree. C., as shown in FIG. 6(D), the outer resin 10 is hardened, and the outer member 7 is formed around the periphery of the ceramic element 2 and the cavity 8. At the same time, a part of the wax 9 absorbed into the outer resin 10 is dispersed to the outside. Then, the lead terminals 6a and 6b are cut off from the frame (not shown).
In the conventional method shown in FIGS. 5 and 6(A)-(D), since a flux containing an activator of the ionic halogen group is used in the soldering, the residual flux remaining after soldering has a strong corrosivity. Thus, the residual flux corrodes the drawing electrodes and the vibrating electrodes of the ceramic element and the lead terminals, adversely affects the electrical characteristic of the oscillator, and reduces the reliability of the product. In order to maintain the reliability of the product, in the conventional method shown in FIGS. 5 and 6(A)-(D), the residual flux remained after soldering is cleaned with a solvent containing chlorine. However, the solvent containing chlorine destroys the ozone layer and thus it has been decided that the use thereof will be prohibited in the near future.